Infrared microspectroscopy can be used to provide an infrared spectrum of liquid and solid materials. In a typical apparatus of this type a source of infrared energy is directed through the specimen which is supported on an optically clear disc-like window, and mirrors are employed to vary the wavenumber or length of the beam and generate an infrared spectrum of a specific area of the specimen. The window used in an apparatus of this type is generally composed of a crystal such as KBr, BaF.sub.2, or the like, which is capable of transmitting infrared radiation.
When analyzing a solid specimen, such as animal or plant tissue, paint flakes, or the like, a thin section of the specimen, generally having a thickness in the range of 5 to 15 microns, is mounted on the window. It is important that the specimen have a thickness in the above-mentioned range, for if the specimen is too thick, distorted spectra are obtained, in which strong bands flatten out and weak bands are disproportioned. It is also important to hold the specimen flat against the window, and this is generally accomplished by either clamping the specimen between two windows or discs, or holding the specimen taut against a surface of the window through use of tape or the like.
When analyzing a liquid specimen, a thin film of the liquid is applied to the surface of the disc-like window. However, the conventional windows, as used in the past will not tolerate water or acidic materials, for the water or acidic materials will attack the window, which will cause loss of specimen integrity. The procedure, as used in the past, for analyzing aqueous solutions, has been to initially distill off the water to obtain a solid or viscous liquid and then neutralize the residue. The residue is then extracted with a solvent which will not attack the window. The solvent solution is then placed on a surface of the window and an infrared spectrum can them be obtained. However, the spectrum of the solvent itself, as well as the spectrum of the window, must be deducted from the composite spectrum. It has also been noted that when using this extraction method, there is some loss of specimen integrity, due to the processing involved.
As a further problem, the disc-like windows, as used in the past to support the specimens,,are very expensive and in most cases are discarded after use, or alternately, require costly surface repolishing before re-use.